The Claus process continues to be the most widely used process worldwide to convert hydrogen sulfide that has been stripped from acid gas or refinery off-gas streams to elemental sulfur. It consists of a two-stage process: the first process stage is thermal and the second stage is catalytic. During the thermal process, the H2S is partially oxidized with air in a reaction furnace at high temperatures, e.g., from 1000°-1400° C. Sulfur is formed, but some H2S remains unreacted and SO2 is also formed, as depicted below:2H2S+3O2→2SO2+2H2O  (I)
During the catalytic process, the remaining H2S is reacted with the SO2 at lower temperatures, i.e., about 200°-350° C., over a catalyst to produce additional elemental sulfur, as follows:2H2S+SO2→3Sx+2H2O  (II)
The Claus catalyst which offers improved sulfur conversion over spherical activated bauxite, or alumina, has high surface area, low density and high macroporosity. These properties provide maximum activity for the conversion of sulfur compounds. The art relating to the production of Claus catalysts is well developed, as shown, for example, in U.S. Pat. No. 4,364,858 and the numerous patents cited and discussed there. However, the reaction does not go to completion, even with the best catalyst. For this reason, two or three catalytic stages are used, with sulfur being removed between the stages.
Claus catalyst is deactivated due to lay down of coke and sulfur-containing species causing lowering of sulfur recovery and also polluting the atmosphere by releasing excessive amounts of sulfur dioxide during acid gas flaring. The deactivation of the Claus catalyst is caused by a variety of factors, such as the presence of accompanying hydrocarbons, particularly of C-5's and benzene, toluene and xylenes. Sour gases are prone to lay down coke on Claus catalyst due to thermal cracking in the split-flow mode.
Hundreds of tons/year of spent Claus catalyst are produced by gas processing plants, gas-oil separation plants (GOSPs) and natural liquid gas fractionation facilities due to frequent replacement of the alumina catalyst beds. In many instances, the spent catalyst has been disposed of by dumping it in a landfill. The cost of landfilling spent Claus catalyst is generally minimal where the land is available and inexpensive, the principal cost being its transportation.
National and international regulations have provided increased opportunities and economic incentives for the petroleum and gas processing industries to implement waste reduction programs for the purpose of enhancing the environment. The incentives for waste minimization on an international basis have been increased by the ban on the land disposal of untreated wastes from the petroleum industry. As the complexity and cost of waste management and disposal increases, waste minimization becomes a significant priority for industry and government.
The goal of reducing waste material from industrial processes requiring disposal can be accomplished either by regeneration of the material or by finding a new and economical use for the spent Claus catalyst waste material.
In some instances, the regeneration treatment cost has been found to be more expensive than purchasing fresh catalyst and, therefore, regeneration was not economically viable.
Other proposals for utilizing spend catalytic materials in an environmentally acceptable manner can also be found in the prior art. For example, U.S. Pat. No. 5,032,548 and U.S. Pat. No. 5,096,498 recommend the use of catalyst particles within a prescribed size range as a base in large construction projects, such as roads and levees. However, the spent catalyst must also be mixed with hydrated lime, Portland cement and other binders.
The use of spent catalyst fines admixed with concrete is disclosed in U.S. Pat. No. 4,231,801. The use of catalyst particles in the process for manufacturing a Portland cement prior to the burning step is disclosed, but it also teaches the addition of an agglomerating material.
It is therefore a principal object of the present invention to provide a means of economically and beneficially utilizing the spent Claus catalyst in order to provide an alternative to landfill disposal.
A further object of the invention is to provide new uses for spent Claus catalyst that will have a significant favorable environmental and cost-saving impact on those industries that must dispose of the spent catalyst.